Please use this identifier to cite or link to this item: http://doi.org/10.25358/openscience-5635
Authors: Korschelt, Karsten
Title: Inorganic Nanoparticles in Biological Inspired Catalysis and their Practical Applications
Online publication date: 8-Apr-2021
Year of first publication: 2021
Language: english
Abstract: Native enzymes are maybe the most specialized catalysts, which were optimized by nature over thousands of years. They play a crucial role in uncountable biochemical processes and their dysfunctionality usually has serious impact for the superordinated organism. Nevertheless, native enzymes still have sharp limitations, especially in practical applications, beyond their natural occurrence. The practical use of the native or recombinant synthesized catalysts is limited to special pH- and temperature values and accompanied by high production costs. Inspired by the central role of native enzymes in nature, a myriad of researchers is focussed on the exploration of functional and catalytically active enzyme replacements. Recently, various forms of enzyme-mimics, mainly supramolecules, metal complexes and metal oxide nanoparticles, have been reported in literature. The catalytic properties of metal containing nanomaterials within the field of classical heterogeneous catalysis, are well known, but their potentials as enzyme replacements were overlooked for a long time. Such a development in past is quite surprising, because nature was everytime a great model for many researchers and there are many similarities between nanoparticles and native enzymes. Due to their size ranges native enzymes could in general be described as “nano” catalysts. Another important analogy of native enzymes and artificial nanozymes is, that enzyme-catalyzed reactions are formally similar to surface-catalyzed reactions. While the Michaelis Menten theory proposes that an enzyme (E) binds a substrate (S), forming an enzyme substrate complex (ES), which is subsequently transformed to a product (P) and the enzyme (E). The Eley-Rideal-mechanism describes catalytic process of a surface catalyzed reaction with the adsorption of a reactant (R1) onto the catalyst surface (C), while the second reactant (R2) directly interacts with the adsorbed species (from gas phase or from solution), followed by desorption of the product (P). This similarity is representing the basic idea behind the nanozyme research. In the first years of exploring nanoparticles in the biocatalytic context, various enzyme mimics like peroxidases, catalases and superoxide dismutases were reported. Recently, especially the exploration of practical applications, mostly in vitro and in vivo studies, where the focal point of research.The present thesis enables an insight into recent and current enzyme mimetic literature, focussing on possible practical applications. Studies conducted within the scope of this thesis will be described and discussed in context of the existing status quo in literature. 1) Glycine functionalized copper (II) hydroxide nanoparticles were synthesized on a simple and large-scale route, executed at room temperature in an aqueous solution. The nanoparticles were able to mimic the catalytic activity of native CuZn superoxide dismutase enzyme. In context of investigating the intrinsic superoxide dismutase-like activity, a novel calculation method for nanozymes was established, enabling the normalization of activities to one active surface site. Deeper studies of the reaction mechanism indicated properties of a catalytic process, rather than a simple oxidation of copper surface atoms. Glycine functionalized copper(II) hydroxide nanoparticles applied to commercial filter cigarettes were able to reduce reactive oxygen species in cigarette smoke. 2) A hematite containing polyvinyl alcohol fiber mesh was prepared via electrospinning and free alcohol groups of the mesh were crosslinked with glutaraldehyde. As-prepared meshes were not soluble in water, but swelling properties enabled a substrate diffusion into the fibers. Embedded hematite nanoparticles still exhibited a catalase-like activity, comparable to native catalase and not electrospun nanoparticles. The fibers were able to protect fibroblasts against cell death, triggered by elevated hydrogen peroxide concentrations.3) Native enzymes like the vanadium haloperoxidases are important biocatalysts. The group haloperoxidases catalyse the reaction of X- (X = Br, Cl, I) and H2O2 which forms hypohalous acids HOX. Formed HOX can halogenate organic compounds in different follow-up reactions. The formation of HOX can prevent the biofilm formation because of their biocidal activity. In this project a nanoceria containing polyvinyl alcohol fiber mesh was synthesized and the haloperoxidase-like activity was tested. It was found, that the prepared fibers still show a high activity in a haloperoxidase-like reaction. It was further demonstrated that the nanoparticle containing fibers show an improved stability, which was tested via atomic force microscopy. The catalytic activity and the mechanical stability enable that nanoceria containing fibers could practically be used to prevent the biofilm formation and to overcome the limitations of “free” nanoparticles like the reduction of active material with time due to leaching effects. 4) Native jack bean urease, an urea splitting enzyme, was the first native enzyme, which could be crystallized. Because of the reaction products ammonia and carbonate, generated in aqueous solution, a kinetic study of urease or possible urease mimics is time-consuming and not trivial. Hence, a time efficient lab assay was developed and nanoceria as the first nanozyme with urease-like activity was reported. In addition to the kinetic studies of cerium oxide nanoparticles, the influence of the surface ratio of cerium(III)/cerium(IV) was investigated, by synthesizing lanthanum doped ceriumoxide nanoparticles. It was found, that a lower ratio, which is synonymous with a higher cerium(IV) concentration at the nanoparticle surface, lead to a higher activity. In further analysis the influence of copper(II) ions, one of the strongest urease inhibitor, was investigated. We found, that copper(II) ions neither have influence on the catalytic activity of cerium oxide nanoparticles, nor on the lanthanum doped cerium oxide nanoparticles.5) Various single metal oxide particles, like molybdenum, tungsten and vanadium oxide, were synthesized and their catalytic activity in an sulfide oxidation reaction, was investigated. To determine the catalytic activity of the different catalysts, kinetic studies were conducted using methyl phenyl sulfide as model substrate. The organic sulphide was oxidized with hydrogen peroxide as green and biocompatible oxidation agent in an aqueous media. We found, that the catalytic activity and the product formation could be enhanced with the use of molybdenum and tungsten mixed oxide particles. Mixed oxide particles with different Mo:W ratios were synthesized and their ability of facilitating the oxidation of methyl phenyl sulfide was investigated. We found, that all mixed oxide particles catalyzed the oxidation of methyl phenyl sulfide completely selective into the methyl phenyl sulfoxide or the methyl phenyl sulfone in presence of one or three equivalents of hydrogen peroxide. In addition to kinetic studies we investigated the influence of different functional groups of the organic sulfide and the effect of steric hindrance. In general, high turnovers could be achieved.
DDC: 540 Chemie
540 Chemistry and allied sciences
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 09 Chemie, Pharmazie u. Geowissensch.
Place: Mainz
ROR: https://ror.org/023b0x485
DOI: http://doi.org/10.25358/openscience-5635
URN: urn:nbn:de:hebis:77-openscience-4922d876-f0dc-484d-9f9d-c297527b76dd8
Version: Original work
Publication type: Dissertation
License: CC BY-ND
Information on rights of use: https://creativecommons.org/licenses/by-nd/4.0/
Extent: xxxii, 250 Seiten, CCLI-CCLXX Seiten, Illustrationen, Diagramme
Appears in collections:JGU-Publikationen

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